DESCRIPTION The ultimate goal of this research is to understand mechanisms underlying the interactive role of microglia and neurons in neuronal injury and neurodegenerative disease. The unifying theme is the reciprocal regulation of protein phosphorylation systems in microglia and neurons in neuronal injury and neurodegenerative disease regarding key early events governing the functional response of each cell type, and thus represent critical therapeutic intervention points. The specific hypotheses addressed are that regulation of microglial tyrosine phosphorylation is a seminal and necessary step in the response of microglia to neuronal injury, and that microglia activated by amyloid peptides secrete soluble factors which mediate phosphorylation of neuronal tau proteins to an AD like state via identifiable potentially novel pathways. An animal model of neuronal degeneration in which microglia exhibit a robust upregulation of tyrosine phosphorylation prior to any other sign of activation, together with infusion of tyrosine kinase inhibitors, will be used to ask whether blocking tyrosine phosphorylation prevents the conversion of microglia from the ramified to the ameboid form. Western blot and in gel kinase analyses will be used to examine the dynamics, substrates and enzymes involved in this response Hippocampal neurons in culture will be used to examine regulation of tau phosphorylation by factors derived from microglia activated in the presence of amyloid peptides. Current data indicate that this phosphorylation may be effected by novel kinases, and Western blot and in gel kinase assays will be used to confirm and extend these results. Kinase inhibitors will be used to ask whether release of microglial factors is dependent on tyrosine phosphorylation.